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Quantitative analysis of WC stars: constraints on neon abundances from ISO-SWS spectroscopy

Dessart, Luc and Crowther, Paul A. and Hillier, D. John and Willis, Allan J. and Morris, Patrick W. and van der Hucht, Karl A. (2000) Quantitative analysis of WC stars: constraints on neon abundances from ISO-SWS spectroscopy. Monthly Notices of the Royal Astronomical Society, 315 (2). pp. 407-422. ISSN 0035-8711. doi:10.1046/j.1365-8711.2000.03399.x.

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Neon abundances are derived in four Galactic WC stars—γ² Vel (WR 11, WC8+O7.5III), HD 156385 (WR 90, WC7), HD 192103 (WR 135, WC8) and WR 146 (WC5+O8)—using mid-infrared fine-structure lines obtained with ISO-SWS. Stellar parameters for each star are derived using the non-local thermodynamic equilibrium model atmospheric code of Hillier & Miller, together with ultraviolet (IUE), optical (INT, AAT) and infrared (UKIRT, ISO) spectroscopy. In the case of γ² Vel, we adopt very recent results from De Marco et al., who followed an identical approach. ISO-SWS data sets reveal the [Ne III] 15.5-μm line in each of our targets, while [Ne II] 12.8 μm, [S IV] 10.5 μm and [S III] 18.7 μm are observed solely in γ² Vel. Using a method updated from Barlow et al. to account for clumped winds, we derive Ne/He=(3–4)×10⁻³ by number, plus S/He = 6×10⁻⁵ for γ² Vel. Neon is highly enriched, such that Ne/S in γ² Vel is eight times higher than cosmic values. However, observed Ne/He ratios are a factor of 2 lower than predictions of current evolutionary models of massive stars. An imprecise mass loss and distance were responsible for the much greater discrepancy in neon content identified by Barlow et al. Our sample of WC5–8 stars span a narrow range in T_* ( = 55–71 kK), with no trend towards higher temperature at earlier spectral type, supporting earlier results for a larger sample by Koesterke & Hamann. Stellar luminosities range from 100 000 to 500 000 L_⊙, while 10^(-5.1) ⩽ Ṁ /(M_⊙ yr⁻¹) ⩽ 10^(-4.5), adopting clumped winds, in which volume filling factors are 10 per cent. In all cases, wind performance numbers are less than 10, significantly lower than recent estimates. Carbon abundances span 0.08 ⩽ C/He 0.25 by number, while oxygen abundances remain poorly constrained.

Item Type:Article
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URLURL TypeDescription Paper
Dessart, Luc0000-0003-0599-8407
Crowther, Paul A.0000-0001-6000-6920
Hillier, D. John0000-0001-5094-8017
Morris, Patrick W.0000-0002-5186-4381
Additional Information:© 2000 RAS, MNRAS. Accepted 2000 January 24. Received 2000 January 21; in original form 1999 November 23. This work is based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, The Netherlands and the United Kingdom) with the participation of ISAS and NASA. Theoretical predictions presented here were possible only as a result of the Opacity Project, led by Professor Michael Seaton. Thanks are due to Dr Tim Harries for observing WR90 on our behalf at the AAT. LD would like to acknowledge financial support from the UCL Perren Fund. PAC acknowledges financial support from a Royal Society University Research Fellowship. DJH gratefully acknowledges support by NASA through grant number NAG5-8211. The Anglo-Australian Telescope, Isaac Newton Telescope and UK Infrared Telescope are operated by the Anglo-Australian Observatory, Isaac Newton Group and Joint Astronomy Centre, respectively, on behalf of the Particle Physics and Astronomy Research Council.
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University College LondonUNSPECIFIED
Subject Keywords:stars: abundances, stars: evolution, stars: fundamental parameters, stars: Wolf-Rayet, infrared: stars
Issue or Number:2
Record Number:CaltechAUTHORS:20210122-185027236
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Official Citation:Luc Dessart, Paul A. Crowther, D. John Hillier, Allan J. Willis, Patrick W. Morris, Karel A. van der Hucht, Quantitative analysis of WC stars: constraints on neon abundances from ISO-SWS spectroscopy, Monthly Notices of the Royal Astronomical Society, Volume 315, Issue 2, June 2000, Pages 407–422,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:107691
Deposited By: Rebecca Minjarez
Deposited On:28 Jan 2021 16:43
Last Modified:16 Nov 2021 19:05

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